Ion beam implanters are widely used in the process of doping of semiconductor wafers. An ion beam implanter generates an ion beam comprised of desired species of positively charged ions. The ion beam impinges upon an exposed surface of a semiconductor wafer workpiece thereby “doping” or implanting the workpiece surface with desired ions.
One type of ion beam implanter uses a rotating, translating disk-shaped support on which workpieces are mounted. A plurality of semiconductor workpieces are mounted on the disk-shaped support. The support is supported in an implantation chamber of an end or implantation station of the ion beam implanter. The rotation of the support allows each of the plurality of workpieces to be exposed to the ion beam during a production run.
To achieve proper implantation depth and dosage and to avoid certain detrimental effects such as channeling, an implantation orientation of a workpiece needs to be able to be adjusted with respect to two axes which are orthogonal to the direction of the ion beam. If the ion beam is assumed to travel along the z axis, the workpiece needs to be able to be tilted or angled with respect to both the x (horizontal) axis and y (vertical) axis. Tilting the workpiece implantation surface with respect to the x axis is referred to as changing the alpha (α) angle of the workpiece and tilting the workpiece implantation surface with respect to the y axis is referred to as changing the beta (β) angle of the workpiece.
To change implantation orientation, the implantation station must be able to pivot with respect to ion beam forming and directing apparatus of the implanter, that is, the portion of the implanter that forms and directs the ion beam prior to the beam entering an interior region of the implantation station. Since the implantation station must move with respect to the beam forming and directing apparatus of the implanter and further since the implantation station interior region and the interior region defined by the beam forming and directing apparatus are both evacuated, a flexible vacuum seal or bellows must be provided between implantation station and the beam forming and directing apparatus.
Because the bellows is adjacent the implantation station, over time, the bellows interior becomes coated by implantation byproducts, that is, undesirable particles and flakes of material that are generated from the implantation process and which subsequently float around in the interior regions of the implantation station and the beam forming and directing apparatus. Such implantation byproducts include materials sputtered off workpieces and other surfaces which the ion beam impinges. When the bellows are subsequently exercised or flexed to change the position of the implantation station, the implantation byproducts deposited on the bellows interior are prone to break off or dislodge and float around within the interior regions of the implantation station and the beam forming and directing structure. Such dislodged flake and particle byproducts may ultimately be deposited on the workpieces causing contamination of the workpieces and degrading the uniformity and quality of the implantation. Further, another source of implantation byproducts in the form of silicon dust from pieces of broken workpieces are often trapped in the convolutions of bellows. In addition to generating particles that may be deposited on workpieces, such pieces may also cause vacuum leaks.
Cleaning a bellows is difficult and often ineffective. Moreover, replacing the bellows is costly. What is needed is a device that will shield the bellows from implantation byproducts. What is also needed is a device that will reduce workpiece contamination resulting from implantation byproducts. What is additionally needed is a device to prolong the life of the bellows